Indirectly heated cathode



Nov.` 3, 1936. H. ROTHE INDIREGTLY HEATED cATHoDE iNvENToR HORST ROTHE Filed Aug. 4, 1932 ATTORNEY Patented Nov. '3, 1936 n UNITED STATES PATENT OFFICE INDIRECTLY HEATED CATHODE Horst Rothe, Berlin, Germany, assigner to Telefunken Gesellschaft fr Drahtlose Telegraphie m. b. H., Berlin, Germany, a corporation of Germany Application August 4, 1932, Serial No. 627,428 In Germany August 7, 1931 3 Claims. (Cl. Z50-27.5)

This invention relates to thermionic tubes, and bodies have no internal bores they can be readily more particularly to indirectly heated cathodes formed by pressing mechanically. The heater for use in such tubes. Wire may be h-airpin shaped, for instance, and is As known in the prior art, and in present-day mechanically supported in the slots of the thick- 5 form of constructions, indirectly heated cathcned portions. The means for mechanically supodes are provided with rod-shaped cores of inporting the heater wire may be improved by sulation material, such as alumina, with slender closing the slots with a highly refractory cement bores into which the heater, for instance, a wire hardened upon the heating of the filament during or a spiral or loop of tungsten is threaded. Beexhaustion. The number and the cross-section cause of the high thermal capacity and the low of the thickened portions of the insulation body 10 heat conducting power of the insulation matemust be so chosen that the heater wire is easily rials the aggregate starting time in heating such held or supported in its position symmetric-ally cathodes amounts to about 1 minute. It has been in reference to the outer cathode tubelet and that previously suggested to reduce this heating time no electrically conducting paths with the same CII l5 by having some parts of the insulation body will be produced. l5

ground away so that the heater element may be What is claimed is: supported by the insulation material only locall. An indirectly heated cathode comprising an 1y or in some places, while being free or exposed electron emitting tubular member, a core of otherwise so that it is enabled to radiate the heat insulating material centrally arranged within freely and directly to the surrounding cathode and spaced from the inner wall of the tubular 20 sleeve or shell consisting, for instance, of a nickel member, a plurality of circular discs of insulating tube fitted over the insulating core. However, material interposed between said insulating core the work of grinding away some of the insulaand said inner wall, each disc being provided tion is attended with serious diiiiculties. with radial slots which extend from the surface Now, in order that the advantage offered by of the central core to the disc periphery and 25 the fact that at least part of the heater body is which are in alignment with corresponding slots exposed, may be combined with ease of manuof the remaining discs, and a lamentary heater facture. the insulation body or core is constructed wire threaded through such slots. as illustrated in Figs. 1 and 1A in accordance with 2. An indirectly heated cathode comprising a one form of the invention. Figs. 2 and 2A distubular electron emitting member, an insulating 30 close a second modification in accordance with core coaxially arranged within the tubular memthis invention. In the modification shown in ber and provided at each end with an enlarged Figs. l and 1A the insulation body or core concircular insulating disc adapted to iit snugly withsists essentially of a slender or thin central part in the tubular member, said circular discs having a of circular cross-sectional form, and in the diametrically opposite radial notches which ex- 35 modication shown in Figs. 2 and 2A the central tend all the way to the disc peripheries, the core a is flat or shaped in the form of a recnotches of one disc being longitudinally aligned tangle. In each modification the insulation body with the notches of the other, and a hairpin or core is provided with thickened portions lr heater wire threaded through s-aid notches.

at both ends and also at one or more intermediate 3. An insulating core for electron discharge 40 parts thereof, the diameter thereof correspondcathode heaters comprising an insulating core ing exactly to the inner diameter of the .nickel provided along its length in spaced relation with tubelet c fitted thereover. The raised or heavier enlarged circular insulating discs, said circular portions are provided with radially extending discs having radial notches which extend lall the slots at two or more opposite points in a longiway to the disc peripheries, and the notches of 45 tudinal direction of the insulation body and one disc being longitudinally aligned with the may be formed by pressure, said slots being just notches of the other. large enough to receive the heater wire provided HORST ROIHE. for heating the cathode. Since these insulation 

